The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
For many advanced mobile platforms, for example, aircraft and missiles, an engine exhaust nozzle with a fixed geometry is often desired to reduce costs, weight, complexity and to improve survivability. However, many of these systems require nozzle throat area variation, thrust vectoring, and efficient mixing of cool bypass air and hot core flow air. These requirements are difficult to meet with presently available, fixed nozzle geometry designs.
Several key design issues exist when dealing with nozzles with variable throat area. Complexity of the design often limits the platform-to-platform transition for existing platforms, thus making it difficult or impossible to use a particular variable throat area nozzle for two or more common mobile platforms (for example, for two or more different models of aircraft). Also, achieving throat area control, thrust vectoring and efficient mixing typically requires separate systems that add cost and weight, as well as potentially decrease reliability. At present, there are generally two categories of nozzle throat area control devices, one being mechanical systems that involve linkage for mechanically adjusting nozzle throat area, and the other involving fluid property manipulation systems. Fluid property manipulation systems typically involve fluid injection into the throat of a flow nozzle in an attempt to alter the effective throat area of the flow nozzle.
Mechanical throat area control systems typically require rigidity in the nozzle/air frame integration since these system designs require the use of kinematic linkages. The additional parts required in a mechanical design tend to increase the system costs and weight. Moving parts can also have a negative impact on compatibility of different nozzle designs for different platforms. Furthermore, previously developed kinematic linkage systems for controlling throat area of a flow duct or a flow nozzle often do not simultaneously achieve throat area control, thrust vectoring and mixing.
Existing fluid property manipulations systems are often designed such that the fixed geometry represents the largest throat area required for afterburn (AB) nozzle operation. Local fluid properties within the flow nozzle are then altered through fluidic injection to change the effective nozzle throat area. These systems require bleed air from the engine to run in “a dry mode”. This can rob the engine of critical efficiency during the longest segment of most missions, which is typically the cruise segment.
Existing fluidic vectoring designs often also develop compressive shock waves in the divergent section of a flow nozzle, which inefficiently turn supersonic flow. Throat skewing systems require short divergent sections to maintain vectoring efficiency. The short divergent section causes the divergent angle to be large for large area ratio nozzles, thus resulting in rapid expansion of the exhaust flow, which degrades efficiency. Therefore, existing fluidic vectoring designs are typically only applicable to low area ratio nozzles.
Previous systems do not address the need for cross-sectional area control, mixing, and vectoring simultaneously. Nor do previous fluidic nozzles circumvent the use of bleed air during the cruise portion of the mission. Thus, it would be highly desirable to incorporate the above capabilities into a single platform of fixed geometry.